Whooo, just what exactly are the Barbican's curators on? I could have done with some of it to get round their latest offering to the taxpaying public. Following hot on the heels of Seduced: Art and Sex from Antiquity to Now, we have the Martian Museum of Terrestrial Art. Either this is a very big and very expensive tease, or I am severely deficient in the arts of Martian irony.

The premise of this extravaganza is as follows: Martians have arrived on Earth to find earthlings obsessed with this thing called “art”. They study the phenomenon and remove a number of objects which they take back to Mars and arrange in a museum for the education and enjoyment of Martians. I'm feeling distinctly queasy already.

Here are the bald facts: 200 objects, mainly sculptures, mostly heavily conceptual and in many cases second rate, plus some works on paper, photographs, video installations ... oh, yes, and a sound work by Louise Lawler which is an eight-minute recording of bird song; a sort of tape of Louise's best bird impressions, but with a difference. She has recorded the names of 28 artists, blameless people such as Donald Judd, Anselm Keifer and Sol Lewitt, and turned the sounds of their names into bird calls. So what you get is a sort of recitative of “caw caw”; but apparently, and perhaps only if you're a Martian, it sounds like “d-o-n-a-l-d-j-u-d-d ... .a-n-s-e-l-m-k-e-i-f-e-r ..” and so on.

On arrival, visitors are greeted with “the motherboard” from which branch out “circuits” (earthlings will recognise these as strips of copper that have been laboriously superglued to the floor) that lead to the four sections of the show, categorised as Kinship and Descent, Ritual, Magic and Belief, and Communication.

Ah yes. The Duchamp urinal. There's a bronze version of this in the Kinship and Descent section, made by Sherrie Levine. Actually, it's the first thing you see and it's very shiny: the lowly artefact raised to a higher art-form. The Martians reckon that this was made in worship of an earlier artist called Marcel Duchamp. They may well be right. I say it's all his fault.

Francesco Manacorda, with Lydia Yee one of the curators responsible for the exhibition, explains that the idea came from the first chapter of a book called Kant after Duchamp by the Belgian art historian Thierry de Duve, in which an imaginary anthropologist from outer space sets out to inventory “all that is called art by humans”.

I am struggling to digest all this when I am handed an audio guide in which a deadpan BBC voice enlightens me on the item Poussière de poussière de l'effet Cimabue: La Vierge aux anges (“Dust of dust from the Cimabue effect: Virgin with Angels”). This is by Robert Filliou, was made in 1977, and consists of a little cardboard box containing a piece of dusty cotton wool. Stapled to the open lid is a Polaroid of a man dusting the frame of Cimabue's painting. The Martians believe that this is magic dust and that when earthlings gaze at great paintings for a long time they are actually looking at the dust on the surface.

Wait. It gets weirder. Nearby is a pig, stuffed and tattooed on its back with a picture of Princess Ariel from The Little Mermaid, and signed “Walt Disney”. Wim Delvoye came up with that in 2006.

I walk around wondering if I am just a very crusty old critic. I smile at Brian Jungen's totem pole made of red and blue golf bags, balanced one on top of another, the bold colours and protruding zip-on pockets making it look like a wonderfully exuberant Native American creation.

I enjoy Jeffrey Vallance's 1979 project, Cultural Ties, for which he wrote to the world's heads of state, sending each one a tie and asking for one of their own in return. Many obliged. The South Koreans, the Singaporeans, the Somalis and others played the game and sent back fabulous kipper ties with amused accompanying letters. Ferdinand Marcos of the Phillipines wrote back without enclosing a tie. He kept Vallance's, perhaps for a collection to rival that of his wife Imelda's shoes.

The Queen returned Vallance's tie with a grim little letter from a lady-in-waiting explaining that Her Majesty could not accept gifts from people not known personally to her.

I find John Bock's blood and gore video unwatchable. I walk on wondering if Bock needs therapy, or whether his art is his therapy. And as for Luis Jacob, well, the Martians were baffled, and so am I. His video is called A Dance for Those of Us Whose Hearts Have Turned to Ice, and it shows a man, presumably Jacob himself, dancing naked, but for a fur hat and shoes, in the snow.

Damien Hirst's fish (Isolated Elements Swimming in the Same Direction for the Purpose of Understanding, 1991) lined up all facing the same way in their formaldehyde coffins, pale and green, their wide eyes dead dull, makes us think - in this new context - of a prehistoric cave painting, or some magic ritual designed to assure a successful fishing hunt.

And then I find Bruce Nauman represented with his 1968 neon tube writing, My Name as Though It Were Written on the Surface of the Moon. This is in the Communication category, where the Martians imagine him trying to communicate with other worlds. Nauman has worked with anthropology in art and, of course, this show is all about approaching contemporary Western art as an anthropologist (or an alien) might. It can reveal new perspectives.

“We have taken examples from Western contemporary art, from the past 50 years,” says Manacorda, “and we are trying to analyse these works as if they were alien objects; just as anthropologists have tried in the past to analyse and understand tribal or primitive art which is unknown and for which they have no frames of reference.

“In some cases the Martians, because of gaps in their knowledge, have made inappropriate categorisations, or misinterpreted objects.”

There's Cher as Che Guevara by Scott King, for example, in the Icons section. And in the exhibition catalogue, presented as an Encylopaedia of Terrestrial Art, there are line drawings of some of the objects showing how they might have been used by earthlings in imagined rituals. Barbara Hepworth, for example, appears in a drawing finishing off her beautiful 1957 Icon as if it is the sculpted head of an alien dignitary.

Is it all worth it? For a start they could have got hold of some better conceptual art. I would have liked to see what the Martians made of Tracey Emin's bed or Sarah Lucas's fried eggs and kebab. But perhaps they're giving other artists' egos a spot in the sun for a change. Perhaps they have succeeded in making foreign what had seemed familiar, in making us think afresh about this thing called conceptual art.

It's good for a laugh as long as you don't get too caught up in the intellectual theorising behind it (page 194 onwards in the catalogue). Received notions have been overturned. The show is highly Surrealist and, in the best traditions of Surrealism, it is absurd. I give them high marks for daring.

Martian Museum of Terrestrial Art is at the Barbican Art Gallery, London EC2 (020-7638 4141), from Thurs until May 18

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